【Clear】 , 【transparent】 , 【translucent】 , 【lucid】 , 【pellucid】 ,  【diaphanous】 , 【limpid】 are comparable when they mean having the property of being literally or figuratively seen through.

Something is 【clear】 which is free from all such impediments to the vision as clouds, mist, or haze ( 【clear】 air) or from muddiness, cloudiness, or turbidity ( 【clear】  glass) ( 【clear】 crystals) or from obscurity, vagueness, or indistinctness of any sort ( 【clear】 thinking).

Something is 【transparent】 which is either so 【clear】  or so thin that objects can be easily seen or perceived through it.

Something is 【translucent】 which admits the passage of light through it but which does not permit a 【clear】 sight of what lies beyond.

Something is 【lucid】 (see 【CLEAR】  2) which is both 【transparent】 and luminous; this use is chiefly literary.

Something is 【pellucid】 which is 【clear】 as crystal.

Something is 【diaphanous】 which is so delicate and gossamerlike in texture that it is almost 【transparent】 or is actually 【translucent】 .

Something is 【limpid】 which has the soft clearness of or as if of pure water.